Measurements of the effect of surface slant on perceived lightness

Caterina Ripamonti, Marina Bloj, Robin Hauck, Kiran Mitha, Scott Greenwald, Shannon I. Maloney, David H. Brainard

Research output: Contribution to journalArticlepeer-review

68 Scopus citations

Abstract

When a planar object is rotated with respect to a directional light source, the reflected luminance changes. If surface lightness is to be a reliable guide to surface identity, observers must compensate for such changes. To the extent they do, observers are said to be lightness constant. We report data from a lightness matching task that assesses lightness constancy with respect to changes in object slant. On each trial, observers viewed an achromatic standard object and indicated the best match from a palette of 36 grayscale, samples. The standard object and the palette were visible simultaneously within an experimental chamber. The chamber illumination was provided from above by a theater stage lamp. The standard objects were uniformly-painted flat cards. Different groups of naïve observers made matches under two sets of instructions. In the Neutral Instructions, observers were asked to match the appearance of the standard and palette sample. In the Paint Instructions, observers were asked to choose the palette sample that was painted the same as the standard. Several broad conclusions may be drawn from the results. First, data for most observers were neither luminance matches nor lightness constant matches. Second, there were large and reliable individual differences. To characterize these, a constancy index was obtained for each observer by comparing how well the data were accounted for by both luminance matching and lightness constancy. The index could take on values between 0 (luminance matching) and 1 (lightness constancy). Individual observer indices ranged between 0.17 and 0.63 with mean 0.40 and median 0.40. An auxiliary slant-matching experiment rules out variation in perceived slant as the source of the individual variability. Third, the effect of instructions was small compared to the inter-observer variability. Implications of the data for models of lightness perception are discussed.

Original languageEnglish (US)
Article number7
Pages (from-to)747-763
Number of pages17
JournalJournal of vision
Volume4
Issue number9
DOIs
StatePublished - Sep 8 2004
Externally publishedYes

Keywords

  • Lightness
  • Lightness constancy
  • Real objects
  • Scene geometry
  • Surface slant

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems

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